The present embodiments relate to a magnetic resonance antenna.
Magnetic resonance devices may operate with a plurality of different antennas (e.g., coils) for emitting radio-frequency pulses for the purpose of exciting nuclear magnetic resonance and/or for receiving induced magnetic resonance signals. A magnetic resonance device may include a relatively large, permanently installed coil (e.g., a whole-body coil) and a plurality of small local coils (e.g., surface coils). In contrast to the whole-body coil, the local coils serve to provide detailed imaging of parts of the body and/or organs of a patient that are located relatively close to the surface of the body. The local coils are applied directly at a region of the patient that is to be examined.
When such a local coil is used, radio-frequency pulses may be transmitted using the whole-body coil permanently installed in the magnetic resonance device, and the induced magnetic resonance signals are received using the local coil. In order to enable an interaction between the individual coils to be suppressed, the receive coil may be detuned in the transmit phase, and the transmit coil may be detuned in the receive phase. Detuning entails shifting a natural resonance frequency of the respective coil or antenna in such a way that the shifted resonance frequency lies outside a range of an operating magnetic resonance frequency. An antenna detuned in this manner ideally behaves neutrally, with the result that the antenna is transparent to the radio-frequency pulses emitted by the other coil and/or to the induced magnetic resonance signals.
Magnetic resonance antennas having a birdcage structure are widely used as a whole-body coil. Such an antenna has a plurality of parallel-running longitudinal antenna rods arranged on a cylinder-like surface. The parallel-running longitudinal antenna rods are interconnected in radio-frequency terms at ends of the parallel-running longitudinal antenna using antenna ferrules or rings. The longitudinal antenna rods and antenna ferrules may be embodied in an arbitrary shape. The longitudinal antenna rods and antenna ferrules may be formed, for example, by conductor tracks that may be applied on a flexible conductor track foil and arranged in a cylinder shape around a measurement space, in which an examination subject is contained during an examination. In the case of a whole-body coil, for example, the birdcage structure encloses a patient-receiving chamber, in which a patient is positioned during a measurement.
An antenna having a birdcage structure may be detuned by detuning the antenna ferrules, the longitudinal antenna rods, or both. In such a detuning process, a resonant inductance is interrupted or a resonant capacitance bridged and/or short-circuited, for example, using a suitable radio-frequency switching element.
It is known from U.S. Pat. No. 6,943,551 that radio-frequency switching elements are used in order to detune radio-frequency switching elements inside a magnetic resonance antenna, the radio-frequency switching elements being arranged in a region of a geometric center along a length of longitudinal antenna rods of the magnetic resonance antenna.
It is also known that a transformation of a short-circuit via radio-frequency feed cables to an antenna ferrule is effected in order to detune the natural resonance of the magnetic resonance antenna.